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finished example DecomposeOnceByRandomEndomorphism and solved the doc…
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…umentation problem.
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Tschitschibor committed Oct 16, 2020
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2 changes: 1 addition & 1 deletion doc/Doc.autodoc
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@InsertChunk CategoryOfRepresentations

@Subsection One step in the direct sum decomposition
@InsertChunk DecomposeOnceByRandomEndomorphism
@InsertChunk DecomposeOnce

@Subsection Another category of module homomorphisms
@InsertChunk RepresentingC4C4
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30 changes: 17 additions & 13 deletions examples/DecomposeOnceByRandomEndomorphism.g
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#! @BeginChunk DecomposeOnceByRandomEndomorphism
#! @BeginChunk DecomposeOnce

LoadPackage( "CatReps" );

#! @Example
#! @BeginExample
c3c3 := ConcreteCategoryForCAP( [ [2,3,1], [4,5,6], [,,,5,6,4] ] );
#! A finite concrete category
GF3 := HomalgRingOfIntegers( 3 );
Expand All @@ -22,11 +22,14 @@ DecomposeOnceByRandomEndomorphism( nine );
#! fail
#! @EndExample

#! The above shows that our representation <C>nine</C> is indecomposable.
#! The above shows that our representation <C>nine</C> is
#! indecomposable (with a high probability).
#! We use the tensor product to generate another representation
#! <C>fortyone</C>, that is hopefully decomposable.
#! <C>fortyone</C>, that is hopefully decomposable, and
#! inspect the two resulting embeddings <C>iota</C> and
#! <C>kappa</C>.

#! @Example
#! @BeginExample
fortyone := TensorProductOnObjects( nine, nine );
#! <(1)->25, (2)->16; (a)->25x25, (b)->25x16, (c)->16x16>
result := DecomposeOnceByRandomEndomorphism( fortyone );
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#! matrix on the diagonal: A $3\times 3$-matrix from <C>S(kq.a)</C>,
#! a $3 \times 1$-matrix from <C>S(kq.b)</C> and a $1\times 1$-matrix
#! from <C>S(kq.c)</C>. This matches with the source of the
#! natural transformation $\iota$.
#! embedding <C>iota</C>.

#! @Example
#! @BeginExample
Display( iota );
#! A morphism in The category of functors: Algebroid generated by the right quiver q(2)[a:1->1,b:1->2,c:\
#! 2->2] -> Category of matrices over GF(3) defined by the following data:
#! A morphism in The category of functors: Algebroid generated by the
#! right quiver q(2)[a:1->1,b:1->2,c:2->2] -> Category of matrices
#! over GF(3) defined by the following data:
#!
#!
#! Image of <(1)>:
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#! A morphism in Category of matrices over GF(3)
#! @EndExample

#! We can then look at the other factor of the direct sum
#! decomposition, i.e. $\kappa$. The iteration of
#! We can then look at the other embedding of the direct sum
#! decomposition, <C>kappa</C>. The iteration of
#! <C>WeakDirectSumDecomposition</C> will continue then
#! with <C>Source( kappa )</C>. Each time the random
#! endomorphism will decompose the representation by
#! at most a dimension of $3$.
#! endomorphism will decompose the representation,
#! lowering the dimensions of each object at most by $3$.

#! @Example
Source( kappa );
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